A new method, compression-shear test, has been developed for determining the mode II fracture toughness K (sub IIC) of rock. The effect of the specimen thickness B, the dimensionless notch length a/W as well as the notch inclination angle alpha on the determination of K (sub IIC) has been experimentally studied. The results show that the apparent mode II fracture toughness K (sub c) decreases as B and a/W increase and becomes constant when B> or =70 mm (i.e. cubic specimen) and a/W>0.5. The K (sub c) is almost independent of alpha in the range of 65 degrees -75 degrees . The constant K (sub c) is about 2-3 times that of mode I fracture toughness K (sub IC) and can be considered as the true mode II fracture toughness K (sub IIC) of rock.